Beside already mentioned cold boot attacks, there is always the possibility that the hardware or the initial boot loader is tampered such that it records you disc encryption password. You need to protect both.

Your laptop could be turned off and tampered while you are away, as you come back you would wonder a little bit, but just boot it normally. On the next occasion, the laptop is stolen or the stored and otherwise transferred password just used to encrypted the stored data.

If you have not protected the BIOS / the boot order, it is not that complicated to boot an alternative system and to modify the usually not encrypted or otherwise integrity-protected boot loader. Using an external boot loader or TPM could reduce this risk.

See also Laptop tampering and boot loader for some ideas.

Beside already mentioned cold boot attacks, there is always the possibility that the hardware or the initial boot loader is tampered such that it records you disc encryption password. You need to protect both.

Your laptop could be turned off and tampered while you are away, as you come back you would wonder a little bit, but just boot it normally. On the next occasion, the laptop is stolen or the stored and otherwise transferred password just used to encrypted the stored data.

If you have not protected the BIOS / the boot order, it is not that complicated to boot an alternative system and to modify the usually not encrypted or otherwise integrity-protected boot loader. Using an external boot loader or TPM could reduce this risk.

See also Laptop tampering and boot loader for some ideas.